1. Field of the Invention
The invention relates to a trenching plow mounted on a carrier vehicle, such as a tractor. More specifically, the trenching plow has a pair of cutting arms adjacent the lower soil cutting portion of the plow, to provide a shearing action between each arm and the cutting portion of the plow and/or a shearing action between the arms. This greatly enhances the cutting ability of the plow.
2. Description of the Prior Art
In the past, different approaches have been tried to provide trench cutting machines. Common are the chain or wheel cutting trenchers, where a chain having cutting edges is rotated along a blade or wheel, to cut into the soil, see for instance U.S. Pat. No. 3,831,299 (Kelley). These trenchers have high maintenance costs because they have a large number of parts which are under high stress. They are also dangerous to work with, because the return chain, i.e. the part of the chain which is not cutting into the soil, is exposed to the air and thus a potential hazard. These trenchers necessarily produce trenches having vertical sides and have difficulties to work in confined areas.
A further type of trencher employs a rotating shaft having cutting tool bits radially arranged on the shaft, see for instance U.S. Pat. No. 5,224,797 (Vaughan). When the shaft is rotated and forced into the soil, a trench is cut. Trenchers of this type also have high maintenance costs because they have a large number of parts which are under high stress.
A cable laying plow having a root cutting arrangement is shown in U.S. Pat. No. 4,834,581 (Soules, Jr.). The plow has a shank having a longitudinal blade formed in the leading edge of a lower portion of the shank and having a flat transverse cutting surface above the blade. A cutter having a sharpened lower end is movable with respect to the shank into engagement with the flat cutting surface by a double acting hydraulic cylinder. The cutter and the cylinder rod move between parallel mounting flanges of a vehicle, allowing the hydraulic cylinder itself to be attached to the shank above the mounting flanges. The cutter thus moves reciprocally along the leading edge of the plow blade, and any roots or similar obstacles that collect on the leading edge of the plow may be cut off so they are no longer stuck on the leading edge. The cutter does not enhance or help the trench forming effort itself.
A pipe or cable laying vibratory plow is described in U.S. Pat. No. 6,126,363 (Hunter). The plow has a V-shaped blade with two independently oscillating blade arms, that are not connected at their lower ends. Each blade is free to move in the plane of the blade without interference from and independently of the other blade arm. A perceived problem with this construction is the relatively fragile construction, since the blade is only supported at its top, which seems prone to breakage and thus a cause for high cost of operation. Also, the arrangement with the oscillating arms forming a relatively broad V inherently requires a large power input, compared to a more compact one-blade plow.
It is an object of the invention to provide an improved trenching plow, that enhances the shearing action of the plow as it is moved through the soil whilst using few parts and parts that are large enough to withstand severe stress conditions during extended use periods. The trenching plow according to the invention has several advantages over known trenching plows or other machines used for trenching: it leaves a trench with very clean sides, it pries rocks from the ground by efficiently pushing them up from below, the trenching operation can be performed at a higher speed than for known trenchers, the width of the trench can be adjusted easily and quickly, and the side walls may be tapered to prevent side wall cave-in.
In the invention, a trenching plow adapted for attachment to a vehicle is described. The plow comprises an elongated shank having a blade formed along a lower portion of a leading edge of the shank, the blade having a first soil cutting surface along the leading edge, a first cutting arm pivotably arranged at a forward lower portion of one side of the shank generally parallel to the shank and a second cutting arm arranged at a forward lower portion of an opposite side of the shank generally parallel to the shank. Further, a drive means for reciprocating upper portions of the first arm and the second arm is used.
Preferably, the first cutting arm has a short portion, extending forwards and downwards from the pivot axis, and a long portion, extending backwards and upwards from the pivot axis, and the second cutting arm similarly has a short portion, extending forwards and downwards from the pivot axis, and a long portion, extending backwards and upwards from the pivot axis.
In one embodiment of the invention, the first cutting arm and the second cutting arm move in a scissor movement, so that when the first arm is moving with its short portion in a forward direction, the short portion of the second arm is moving in a rearward direction.
Advantageously, the long portion of the first arm is connected to the drive means via a first connecting rod and the long portion of the second arm is connected to the drive means via a second connecting rod. The first connecting rod preferably has a first small end and a first large end, the first small end being connected to the first arm and the first large end being eccentrically connected to the drive means. Similarly, the second connecting rod preferably has a second small end and a second large end, the second small end being connected to the second arm and the second large end being eccentrically connected to the drive means, so that the drive means imparts an eccentric movement to the first large end and the second large end, respectively, causing the first connecting rod and the second connecting rod to move reciprocically in a direction rearwards downwards from the drive means, thus causing the first arm and the second arm to pivot around the pivot axis, preferably in a scissor movement.
The first arm advantageously has a cutting edge arranged at a leading edge of the first arm, and the second arm has a cutting edge arranged at a leading edge of the second arm.
The plow further preferably comprises means to raise and lower the plow with respect to the vehicle.
The plow further advantageously comprises a first feeding means hingedly attached to a trailing edge of the shank, for directing an elongate material to be buried in the trench down into the trench behind the plow. The first feeding means preferably has a top soil displacement means arranged at a top of the first feeding means, for depositing soil moved to the surface of the ground during operation of the plow at either side of the plow. The displacement means advantageously comprises an Archimedean screw and reversible propulsion means, for rotating the screw in a chosen direction of rotation. The top soil displacement means is preferably raised or lowered, with respect to the shank, using a biasing means, preferably a hydraulic cylinder.
The plow further preferably comprises a second feeding means hingedly attached to a trailing edge of the first feeding means, for directing a further elongate material to be buried in the trench down into the trench behind the plow.